Bone marrow is a spongy tissue found inside bones. The bone marrow in the breast bone, skull, hips, ribs, and spine contains stem cells. Stem cells produce the body's blood cells, e.g., leukocytes, that fight infection); erythrocytes, that carry oxygen to and remove waste products from organs and tissues; and platelets, that enable the blood to clot.
Bone marrow, and some of the cells and cell types that are present in bone marrow, have been found to have significant therapeutic efficacy in the treatment of a number of diseases and conditions. For example, stem cells may be separated from the bone marrow composition and may be used in the treatment of many diseases. Filtered marrow itself may be used as a transplant graft in the treatment of leukemia, aplastic anemia, various lymphomas (e.g., Hodgkin's disease), multiple myeloma, certain immunodeficiencies, and a variety of cancers (typically solid tumors, such as breast and ovarian cancer).
The development of plastic blood collection bags has facilitated the separation of donated bone marrow into its various components and analogous products, thereby making these different components available as a transfusion product.
Further, significant improvements in reducing the immunogenicity of bone marrow transplanted into a patient has greatly increased the use of bone marrow as a competent and desirable therapeutic composition.
For these and other reasons, harvesting bone marrow and separating the bone marrow into components has substantial therapeutic and monetary value. This is nowhere more evident than in treating the increased damage to a patient's immune system caused by the higher doses and stronger drugs now used during chemotherapy for cancer patients. These more aggressive chemotherapy protocols are directly implicated in the reduction of the platelet content of the blood to abnormally low levels.
A conventional bone marrow collection procedure may include the following:
(1) Under general anesthesia, a bone marrow aspiration needle is inserted into the iliac crest (the cavity of the rear hip bone) where a large quantity of bone marrow is located. The bone marrow is extracted with a needle and syringe. Several skin punctures on each hip and multiple bone punctures are usually required to extract the requisite amount of bone marrow.
(2) About 10–30 cc of bone marrow are drawn from each bone puncture, and although the total amount drawn is variable (depending primarily on the size of the donor and the concentration of the bone marrow cells), usually about 1 liter and up to 1.5 liters of bone marrow are harvested.
(3) Each syringe of bone marrow drawn from the donor is then individually expressed into an open collection bag or an open container. The collection bag typically includes an anti-coagulant solution such as heparin and/or CPDA-1.
(4) The used syringe is then used to draw anti-coagulant solution into the syringe, the solution is expelled, and the syringe is used again to draw bone marrow. The process is repeated 30–50 times or more until up to about 1.5 liters of bone marrow is harvested.
(5) During or near the end of the collection process, a sample of about 5 cc is then drawn from the collection bag or container, and the amount of stem cells in the sample is either determined or inferred. Harvesting is usually completed when the sample contains about 1–3×108 nucleated cells per kilogram of body weight of the recipient.
(6) The harvested bone marrow composition is then filtered, generally within about 6 to 8 hours of harvesting. The filtration process usually involves a series of filters having different pore size ratings, typically 850μ, 500μ, and 200μ. These filters remove bone fragments, microaggregates, blood clots, and other undesirable debris from the bone marrow composition.
(7) The filtered bone marrow is then processed according to its end use. For example, if the bone marrow will be used in an autologous transplant, the filtered bone marrow will be frozen (cryopreserved) and stored at a temperature between about −80° C. and about −196° C. until the day of the transplant. For allogeneic transplants, the bone marrow will be treated to remove T-cells, then transferred directly to an infuser for administration to the patient.
The existing regimen for harvesting bone marrow is time-consuming and costly. Further, the present state of the art involves the use of open containers and/or open systems.
In view of this, there is a growing need for an efficient system and method for collecting and processing bone marrow, and for harvesting bone marrow in a closed or sealed system.
The devices and methods of this invention alleviate the above-described problems and, in addition, provide a higher yield of superior quality bone marrow.
A problem attendant with the separation of various blood and bone marrow components using a multiple bag system is that the highly valuable components become trapped in the conduits connecting the various bags and in the various devices that may be used in the system. Conventional processing and storage techniques contribute to these problems. For example, air, in particular oxygen, present in stored blood and blood components, or in the storage container, may lead to an impairment of the quality of the blood components, and may decrease their storage life. More particularly, oxygen may be associated with an increased metabolic rate (during glycolysis), which may lead to decreased storage life, and decreased viability and function of whole blood cells. For example, during storage red blood cells metabolize glucose, producing lactic and pyruvic acids. These acids decrease the pH of the medium, which in turn decreases metabolic functions. Furthermore, the presence of air or gas in the satellite bag may present a risk when a patient is transfused. For example, as little as 5 ml of air or gas may cause severe injury or death. Despite the deleterious effect of oxygen on storage life and the quality of bone marrow blood and bone marrow components, the prior art has not addressed the need to remove gases from bone marrow processing systems during collection and processing.
Because of the high cost and limited availability of bone marrow components, a device comprising a porous medium used to deplete leucocytes from biological fluid should deliver the highest possible proportion of the component present in the donated bone marrow. An ideal device for the filtering or leucocyte depletion of bone marrow would be inexpensive, relatively small, and be capable of rapidly processing the components obtained from about one unit or more of biological fluid (e.g., donated bone marrow), in, for example, less than about one hour. Ideally, this device would reduce the leucocyte content to the lowest possible level, while maximizing the yield of a valuable blood component while minimizing an expensive, sophisticated, labor intensive effort by the operator of the system. The yield of the bone marrow or a component should be maximized while at the same time delivering a viable and physiologically active component. It may also be preferable that the bone marrow filter or porous medium be capable of removing platelets, as well as fibrinogen, fibrin strands, tiny fat globules, and other components such as microaggregates which may be present in the bone marrow.
Definitions
The following definitions are used in reference to the invention:
(A) Bone marrow or Biological Fluid is the soft tissue within bone cavities, and typically contains whole blood, hematopoietic precursor cells and hematopoietic cells that are maturing into erythrocytes, five types of leukocytes, and thrombocytes. Harvested bone marrow typically includes these components, as well as bone chips, megakaryocytes, stem cells, fat globules, blood clots, fibrin, platelets, among other biological and/or cellular matter. Bone marrow or biological fluid also includes any treated or untreated fluid associated with living organisms, particularly bone marrow, including harvested unseparated (whole) bone marrow, warm or cold bone marrow, cryopreserved bone marrow, and stored or fresh bone marrow, treated bone marrow, such as bone marrow diluted with a physiological solution, including but not limited to saline, nutrient, and/or anticoagulant solutions; one or more bone marrow components, such as stem cells; and analogous bone marrow products derived from bone marrow or a bone marrow component. The biological fluid may include leucocytes, or may be treated to remove leucocytes. As used herein, bone marrow product or biological fluid refers to the components described above, and to similar bone marrow products or biological fluids obtained by other means and with similar properties. In accordance with the invention, each of these bone marrow products or biological fluids is processed in the manner described herein.
A typical harvesting procedure commonly draws up to about 1.5 liters of a composition containing bone marrow from the donor into a bag which contains an anticoagulant to prevent the bone marrow from clotting. However, the amount drawn differs from patient to patient and donation to donation.
(B) Filtered bone marrow: refers to a composition containing bone marrow and stem cells that is suitable for use as a transplant graft or an organ graft. The bone marrow harvested from a donor is treated and processed using various regimens before it is suitable for use as a transplant graft. For example, the harvested bone marrow may be mixed with a nutrient and/or anti-coagulant solution, and may be filtered to remove debris and the like.
(C) Porous medium: refers to the porous medium through which one or more bone marrow, bone marrow components, or biological fluids pass. A typical porous medium is a filter for removing undesirable constituents, such as pieces of bone, microaggregates, blood clots, and the like, from the bone marrow. The bone marrow processing system may optionally include a leucocyte depletion filter or porous medium, which refers generically to any one of the media which deplete leucocytes from the bone marrow or a bone marrow component.
The porous media according to the invention may be connected to a conduit interposed between the containers, and may be positioned in a housing which in turn can be connected to the conduit. As used herein, filter assembly refers to the porous medium positioned in a suitable housing. An exemplary filter assembly may include pore size filter assembly and/or a leucocyte depletion assembly or device. A biological fluid processing system, such as a bone marrow collection and processing system, may comprise porous media, preferably as filter assemblies.